3 #ifndef CDSLIB_CONTAINER_IMPL_SKIP_LIST_MAP_H
4 #define CDSLIB_CONTAINER_IMPL_SKIP_LIST_MAP_H
6 #include <cds/container/details/guarded_ptr_cast.h>
8 namespace cds { namespace container {
10 /// Lock-free skip-list map
11 /** @ingroup cds_nonintrusive_map
12 \anchor cds_nonintrusive_SkipListMap_hp
14 The implementation of well-known probabilistic data structure called skip-list
15 invented by W.Pugh in his papers:
16 - [1989] W.Pugh Skip Lists: A Probabilistic Alternative to Balanced Trees
17 - [1990] W.Pugh A Skip List Cookbook
19 A skip-list is a probabilistic data structure that provides expected logarithmic
20 time search without the need of rebalance. The skip-list is a collection of sorted
21 linked list. Nodes are ordered by key. Each node is linked into a subset of the lists.
22 Each list has a level, ranging from 0 to 32. The bottom-level list contains
23 all the nodes, and each higher-level list is a sublist of the lower-level lists.
24 Each node is created with a random top level (with a random height), and belongs
25 to all lists up to that level. The probability that a node has the height 1 is 1/2.
26 The probability that a node has the height N is 1/2 ** N (more precisely,
27 the distribution depends on an random generator provided, but our generators
30 The lock-free variant of skip-list is implemented according to book
31 - [2008] M.Herlihy, N.Shavit "The Art of Multiprocessor Programming",
32 chapter 14.4 "A Lock-Free Concurrent Skiplist"
35 - \p GC - Garbage collector used.
36 - \p K - type of a key to be stored in the list.
37 - \p T - type of a value to be stored in the list.
38 - \p Traits - map traits, default is \p skip_list::traits
39 It is possible to declare option-based list with \p cds::container::skip_list::make_traits metafunction
40 istead of \p Traits template argument.
42 Like STL map class, \p %SkipListMap stores the key-value pair as <tt>std:pair< K const, T></tt>.
44 @warning The skip-list requires up to 67 hazard pointers that may be critical for some GCs for which
45 the guard count is limited (like \p gc::HP). Those GCs should be explicitly initialized with
46 hazard pointer enough: \code cds::gc::HP myhp( 67 ) \endcode. Otherwise an run-time exception may be raised
47 when you try to create skip-list object.
49 @note There are several specializations of \p %SkipListMap for each \p GC. You should include:
50 - <tt><cds/container/skip_list_map_hp.h></tt> for \p gc::HP garbage collector
51 - <tt><cds/container/skip_list_map_dhp.h></tt> for \p gc::DHP garbage collector
52 - <tt><cds/container/skip_list_map_rcu.h></tt> for \ref cds_nonintrusive_SkipListMap_rcu "RCU type"
53 - <tt><cds/container/skip_list_map_nogc.h></tt> for \ref cds_nonintrusive_SkipListMap_nogc "non-deletable SkipListMap"
57 The class supports a forward iterator (\ref iterator and \ref const_iterator).
58 The iteration is ordered.
59 The iterator object is thread-safe: the element pointed by the iterator object is guarded,
60 so, the element cannot be reclaimed while the iterator object is alive.
61 However, passing an iterator object between threads is dangerous.
63 \warning Due to concurrent nature of skip-list map it is not guarantee that you can iterate
64 all elements in the map: any concurrent deletion can exclude the element
65 pointed by the iterator from the map, and your iteration can be terminated
66 before end of the map. Therefore, such iteration is more suitable for debugging purpose only
68 Remember, each iterator object requires 2 additional hazard pointers, that may be
69 a limited resource for \p GC like \p gc::HP (for gc::DHP the count of
72 The iterator class supports the following minimalistic interface:
79 iterator( iterator const& s);
81 value_type * operator ->() const;
82 value_type& operator *() const;
85 iterator& operator ++();
88 iterator& operator = (const iterator& src);
90 bool operator ==(iterator const& i ) const;
91 bool operator !=(iterator const& i ) const;
94 Note, the iterator object returned by \ref end, \ cend member functions points to \p nullptr and should not be dereferenced.
101 #ifdef CDS_DOXYGEN_INVOKED
102 typename Traits = skip_list::traits
108 #ifdef CDS_DOXYGEN_INVOKED
109 protected intrusive::SkipListSet< GC, std::pair<Key const, T>, Traits >
111 protected details::make_skip_list_map< GC, Key, T, Traits >::type
115 typedef details::make_skip_list_map< GC, Key, T, Traits > maker;
116 typedef typename maker::type base_class;
119 typedef GC gc; ///< Garbage collector
120 typedef Key key_type; ///< Key type
121 typedef T mapped_type; ///< Mapped type
122 typedef Traits traits; ///< Map traits
123 # ifdef CDS_DOXYGEN_INVOKED
124 typedef std::pair< K const, T> value_type; ///< Key-value pair to be stored in the map
126 typedef typename maker::value_type value_type;
129 typedef typename base_class::back_off back_off; ///< Back-off strategy
130 typedef typename traits::allocator allocator_type; ///< Allocator type used for allocate/deallocate the skip-list nodes
131 typedef typename base_class::item_counter item_counter; ///< Item counting policy used
132 typedef typename maker::key_comparator key_comparator; ///< key comparison functor
133 typedef typename base_class::memory_model memory_model; ///< Memory ordering, see \p cds::opt::memory_model
134 typedef typename traits::random_level_generator random_level_generator ; ///< random level generator
135 typedef typename traits::stat stat; ///< internal statistics type
138 typedef cds::container::skip_list::implementation_tag implementation_tag;
143 typedef typename maker::node_type node_type;
144 typedef typename maker::node_allocator node_allocator;
146 typedef std::unique_ptr< node_type, typename maker::node_deallocator > scoped_node_ptr;
151 typedef typename gc::template guarded_ptr< node_type, value_type, details::guarded_ptr_cast_set<node_type, value_type> > guarded_ptr;
155 unsigned int random_level()
157 return base_class::random_level();
167 /// Destructor destroys the set object
173 typedef skip_list::details::iterator< typename base_class::iterator > iterator;
175 /// Const iterator type
176 typedef skip_list::details::iterator< typename base_class::const_iterator > const_iterator;
178 /// Returns a forward iterator addressing the first element in a map
181 return iterator( base_class::begin() );
184 /// Returns a forward const iterator addressing the first element in a map
185 const_iterator begin() const
189 /// Returns a forward const iterator addressing the first element in a map
190 const_iterator cbegin() const
192 return const_iterator( base_class::cbegin() );
195 /// Returns a forward iterator that addresses the location succeeding the last element in a map.
198 return iterator( base_class::end() );
201 /// Returns a forward const iterator that addresses the location succeeding the last element in a map.
202 const_iterator end() const
206 /// Returns a forward const iterator that addresses the location succeeding the last element in a map.
207 const_iterator cend() const
209 return const_iterator( base_class::cend() );
213 /// Inserts new node with key and default value
215 The function creates a node with \p key and default value, and then inserts the node created into the map.
218 - The \p key_type should be constructible from a value of type \p K.
219 In trivial case, \p K is equal to \p key_type.
220 - The \p mapped_type should be default-constructible.
222 Returns \p true if inserting successful, \p false otherwise.
224 template <typename K>
225 bool insert( K const& key )
227 return insert_with( key, [](value_type&){} );
232 The function creates a node with copy of \p val value
233 and then inserts the node created into the map.
236 - The \p key_type should be constructible from \p key of type \p K.
237 - The \p value_type should be constructible from \p val of type \p V.
239 Returns \p true if \p val is inserted into the set, \p false otherwise.
241 template <typename K, typename V>
242 bool insert( K const& key, V const& val )
244 return insert_with( key, [&val](value_type& item) { item.second = val ; } );
247 /// Inserts new node and initialize it by a functor
249 This function inserts new node with key \p key and if inserting is successful then it calls
250 \p func functor with signature
253 void operator()( value_type& item );
257 The argument \p item of user-defined functor \p func is the reference
258 to the map's item inserted:
259 - <tt>item.first</tt> is a const reference to item's key that cannot be changed.
260 - <tt>item.second</tt> is a reference to item's value that may be changed.
262 \p key_type should be constructible from value of type \p K.
264 The function allows to split creating of new item into two part:
265 - create item from \p key;
266 - insert new item into the map;
267 - if inserting is successful, initialize the value of item by calling \p func functor
269 This can be useful if complete initialization of object of \p value_type is heavyweight and
270 it is preferable that the initialization should be completed only if inserting is successful.
272 template <typename K, typename Func>
273 bool insert_with( const K& key, Func func )
275 scoped_node_ptr pNode( node_allocator().New( random_level(), key ));
276 if ( base_class::insert( *pNode, [&func]( node_type& item ) { func( item.m_Value ); } )) {
283 /// For key \p key inserts data of type \p value_type created in-place from <tt>std::forward<Args>(args)...</tt>
285 Returns \p true if inserting successful, \p false otherwise.
287 template <typename K, typename... Args>
288 bool emplace( K&& key, Args&&... args )
290 scoped_node_ptr pNode( node_allocator().New( random_level(), std::forward<K>(key), std::forward<Args>(args)... ));
291 if ( base_class::insert( *pNode )) {
298 /// Ensures that the \p key exists in the map
300 The operation performs inserting or changing data with lock-free manner.
302 If the \p key not found in the map, then the new item created from \p key
303 is inserted into the map (note that in this case the \ref key_type should be
304 constructible from type \p K).
305 Otherwise, the functor \p func is called with item found.
306 The functor \p Func may be a function with signature:
308 void func( bool bNew, value_type& item );
313 void operator()( bool bNew, value_type& item );
318 - \p bNew - \p true if the item has been inserted, \p false otherwise
319 - \p item - item of the list
321 The functor may change any fields of the \p item.second that is \ref value_type.
323 Returns <tt> std::pair<bool, bool> </tt> where \p first is true if operation is successfull,
324 \p second is true if new item has been added or \p false if the item with \p key
325 already is in the list.
327 @warning See \ref cds_intrusive_item_creating "insert item troubleshooting"
329 template <typename K, typename Func>
330 std::pair<bool, bool> ensure( K const& key, Func func )
332 scoped_node_ptr pNode( node_allocator().New( random_level(), key ));
333 std::pair<bool, bool> res = base_class::ensure( *pNode,
334 [&func](bool bNew, node_type& item, node_type const& ){ func( bNew, item.m_Value ); }
336 if ( res.first && res.second )
341 /// Delete \p key from the map
342 /** \anchor cds_nonintrusive_SkipListMap_erase_val
344 Return \p true if \p key is found and deleted, \p false otherwise
346 template <typename K>
347 bool erase( K const& key )
349 return base_class::erase(key);
352 /// Deletes the item from the map using \p pred predicate for searching
354 The function is an analog of \ref cds_nonintrusive_SkipListMap_erase_val "erase(K const&)"
355 but \p pred is used for key comparing.
356 \p Less functor has the interface like \p std::less.
357 \p Less must imply the same element order as the comparator used for building the map.
359 template <typename K, typename Less>
360 bool erase_with( K const& key, Less pred )
363 return base_class::erase_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >());
366 /// Delete \p key from the map
367 /** \anchor cds_nonintrusive_SkipListMap_erase_func
369 The function searches an item with key \p key, calls \p f functor
370 and deletes the item. If \p key is not found, the functor is not called.
372 The functor \p Func interface:
375 void operator()(value_type& item) { ... }
379 Return \p true if key is found and deleted, \p false otherwise
381 template <typename K, typename Func>
382 bool erase( K const& key, Func f )
384 return base_class::erase( key, [&f]( node_type& node) { f( node.m_Value ); } );
387 /// Deletes the item from the map using \p pred predicate for searching
389 The function is an analog of \ref cds_nonintrusive_SkipListMap_erase_func "erase(K const&, Func)"
390 but \p pred is used for key comparing.
391 \p Less functor has the interface like \p std::less.
392 \p Less must imply the same element order as the comparator used for building the map.
394 template <typename K, typename Less, typename Func>
395 bool erase_with( K const& key, Less pred, Func f )
398 return base_class::erase_with( key,
399 cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >(),
400 [&f]( node_type& node) { f( node.m_Value ); } );
403 /// Extracts the item from the map with specified \p key
404 /** \anchor cds_nonintrusive_SkipListMap_hp_extract
405 The function searches an item with key equal to \p key in the map,
406 unlinks it from the map, and returns a guarded pointer to the item found.
407 If \p key is not found the function returns an empty guarded pointer.
409 Note the compare functor should accept a parameter of type \p K that can be not the same as \p key_type.
411 The item extracted is freed automatically by garbage collector \p GC
412 when returned \p guarded_ptr object will be destroyed or released.
413 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
417 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
421 skip_list::guarded_ptr gp( theList.extract( 5 ));
426 // Destructor of gp releases internal HP guard and frees the pointer
430 template <typename K>
431 guarded_ptr extract( K const& key )
434 base_class::extract_( gp.guard(), key, typename base_class::key_comparator() );
438 /// Extracts the item from the map with comparing functor \p pred
440 The function is an analog of \ref cds_nonintrusive_SkipListMap_hp_extract "extract(K const&)"
441 but \p pred predicate is used for key comparing.
443 \p Less functor has the semantics like \p std::less but should take arguments of type \ref key_type and \p K
445 \p pred must imply the same element order as the comparator used for building the map.
447 template <typename K, typename Less>
448 guarded_ptr extract_with( K const& key, Less pred )
451 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor > wrapped_less;
453 base_class::extract_( gp.guard(), key, cds::opt::details::make_comparator_from_less<wrapped_less>() );
457 /// Extracts an item with minimal key from the map
459 The function searches an item with minimal key, unlinks it, and returns an guarded pointer to the item found.
460 If the skip-list is empty the function returns an empty guarded pointer.
462 The item extracted is freed automatically by garbage collector \p GC
463 when returned \p guarded_ptr object will be destroyed or released.
464 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
468 typedef cds::continer::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
472 skip_list::guarded_ptr gp( theList.extract_min());
477 // Destructor of gp releases internal HP guard and then frees the pointer
481 guarded_ptr extract_min()
484 base_class::extract_min_( gp.guard() );
488 /// Extracts an item with maximal key from the map
490 The function searches an item with maximal key, unlinks it, and returns a guarded pointer to item found.
491 If the skip-list is empty the function returns an empty \p guarded_ptr.
493 The item found is freed by garbage collector \p GC automatically
494 when returned \p guarded_ptr object will be destroyed or released.
495 @note Each \p guarded_ptr object uses the GC's guard that can be limited resource.
499 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
503 skip_list::guarded_ptr gp( theList.extract_max());
508 // Destructor of gp releases internal HP guard and then frees the pointer
512 guarded_ptr extract_max()
515 base_class::extract_max_( gp.guard() );
519 /// Find the key \p key
520 /** \anchor cds_nonintrusive_SkipListMap_find_cfunc
522 The function searches the item with key equal to \p key and calls the functor \p f for item found.
523 The interface of \p Func functor is:
526 void operator()( value_type& item );
529 where \p item is the item found.
531 The functor may change \p item.second.
533 The function returns \p true if \p key is found, \p false otherwise.
535 template <typename K, typename Func>
536 bool find( K const& key, Func f )
538 return base_class::find( key, [&f](node_type& item, K const& ) { f( item.m_Value );});
541 /// Finds the key \p val using \p pred predicate for searching
543 The function is an analog of \ref cds_nonintrusive_SkipListMap_find_cfunc "find(K const&, Func)"
544 but \p pred is used for key comparing.
545 \p Less functor has the interface like \p std::less.
546 \p Less must imply the same element order as the comparator used for building the map.
548 template <typename K, typename Less, typename Func>
549 bool find_with( K const& key, Less pred, Func f )
552 return base_class::find_with( key,
553 cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >(),
554 [&f](node_type& item, K const& ) { f( item.m_Value );});
557 /// Find the key \p key
558 /** \anchor cds_nonintrusive_SkipListMap_find_val
560 The function searches the item with key equal to \p key
561 and returns \p true if it is found, and \p false otherwise.
563 template <typename K>
564 bool find( K const& key )
566 return base_class::find( key );
569 /// Finds the key \p val using \p pred predicate for searching
571 The function is an analog of \ref cds_nonintrusive_SkipListMap_find_val "find(K const&)"
572 but \p pred is used for key comparing.
573 \p Less functor has the interface like \p std::less.
574 \p Less must imply the same element order as the comparator used for building the map.
576 template <typename K, typename Less>
577 bool find_with( K const& key, Less pred )
580 return base_class::find_with( key, cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor >() );
583 /// Finds the key \p key and return the item found
584 /** \anchor cds_nonintrusive_SkipListMap_hp_get
585 The function searches the item with key equal to \p key
586 and returns an guarded pointer to the item found.
587 If \p key is not found the function returns an empty guarded pointer.
589 It is safe when a concurrent thread erases the item returned as \p guarded_ptr.
590 In this case the item will be freed later by garbage collector \p GC automatically
591 when \p guarded_ptr object will be destroyed or released.
592 @note Each \p guarded_ptr object uses one GC's guard which can be limited resource.
596 typedef cds::container::SkipListMap< cds::gc::HP, int, foo, my_traits > skip_list;
600 skip_list::guarded_ptr gp( theList.get( 5 ));
605 // Destructor of guarded_ptr releases internal HP guard
609 Note the compare functor specified for class \p Traits template parameter
610 should accept a parameter of type \p K that can be not the same as \p value_type.
612 template <typename K>
613 guarded_ptr get( K const& key )
616 base_class::get_with_( gp.guard(), key, typename base_class::key_comparator() );
620 /// Finds the key \p key and return the item found
622 The function is an analog of \ref cds_nonintrusive_SkipListMap_hp_get "get( K const&)"
623 but \p pred is used for comparing the keys.
625 \p Less functor has the semantics like \p std::less but should take arguments of type \ref key_type and \p K
627 \p pred must imply the same element order as the comparator used for building the map.
629 template <typename K, typename Less>
630 guarded_ptr get_with( K const& key, Less pred )
633 typedef cds::details::predicate_wrapper< node_type, Less, typename maker::key_accessor > wrapped_less;
635 base_class::get_with_( gp.guard(), key, cds::opt::details::make_comparator_from_less< wrapped_less >());
645 /// Checks if the map is empty
648 return base_class::empty();
651 /// Returns item count in the map
654 return base_class::size();
657 /// Returns const reference to internal statistics
658 stat const& statistics() const
660 return base_class::statistics();
663 }} // namespace cds::container
665 #endif // #ifndef CDSLIB_CONTAINER_IMPL_SKIP_LIST_MAP_H